The present invention relates to a method and arrangement for analyzing samples or specimens pursuant to the X-ray fluorescence analysis method utilizing a beam detector to detect a secondary beam that originates from the specimen that is to be analyzed and upon which is directed a primary X-ray beam, the path of which is adjustable in at least one axis of freedom.
With one known apparatus (German Patent 36 06 748), the primary beam of an X-ray tube is glancingly guided at an angle of only a few minutes onto the surface of the sample that is to be analyzed, with the adjustment of the effective angle of incidence being undertaken by altering the height of the X-ray tube relative to the specimen that is to be analyzed. An orifice plate inserted directly in the path of the beam after the X-ray tube limits the divergence of the primary beam emitted thereby.
Basically, applicable for this known apparatus as well as in general, upon glancing incidence of X-ray beams onto a planar surface, the primary X-ray beam penetrates only slightly vertically into the body below the surface. For an angle of incidence below the critical or limiting angle of the total reflection, the depth of penetration is even limited to only a very few mm. This known effect makes arrangements for measuring the characteristic fluorescent radiation (secondary radiation or beam) upon glancing incidence of the primary radiation principally into a potentially suitable instrument for determining elements in layers close to the surface. Furthermore, such an effect could also be used for the X-ray fluorescence analysis of extremely small specimens of the order of magnitude of .mu.g, for example dust or residue from solvents, whereby the specimens are placed upon planar polished surfaces that then serve as specimen holders. With such a use, the effect that originates from the surface below the specimen holder, and that under total reflection conditions is extremely low, leads to detection limits of an order of magnitude of pg.
The two uses of the total reflection effect in X-ray fluorescence analysis, in other words not only the analysis of layers near the surface but also the extreme trace analysis of specimens that are placed upon suitable specimen holders, place considerable demands on the technical configuration of total reflection arrangements.
These high demands result from the opposing requirements for a high primary beam intensity (small distance between X-ray tube and the specimen that is to be analyzed) and a high precision of the angular setting (greater distance between X-ray tube and specimen). Due to the physical principle that underlies an X-ray tube, with X-ray tubes that are available today it is merely possible to achieve a primary beam intensity that is very low in comparison to the synchrotron radiation that can be achieved with large accelerators. Already for this reason, it is cogent, when using X-ray tubes as radiation sources for such arrangements, to keep the distances between the anodes thereof and the object that is to be analyzed as low as possible to minimize spacial angle losses.
Furthermore, it has been shown to be advantageous, rather than directing the X-ray beam directly onto the specimen, to indirectly direct the X-ray beam onto the specimen after deflecting the beam via a totally reflecting surface. However, such an arrangement, such as the one disclosed in Schwenke et al U.S. Pat. No. 4,426,717, issued Jan. 17, 1984, limits the adjustability of the angle of incidence upon the specimen in such a way that it cannot be used for the analysis of surfaces that require that the angle of incidence be freely adjustable over a wide range.
It is therefore an object of the present invention to provide a method of analyzing specimens pursuant to the X-ray fluorescence analysis method of the aforementioned general type, with the inventive method making it possible to determine the angle of incidence of the primary beam upon the specimen with a greater precision than was previously possible, whereby any desired angle of incidence of the primary beam upon the surface of the specimen can be set exactly and the angle of incidence of the primary beam can be measured absolutely.
It is another object of the present invention to provide an arrangement for X-ray fluorescence analysis whereby, while maintaining minimal distances between the X-ray tube and the specimen that is to be analyzed, a free adjustability, without affecting one another, of the angle of incidence of the primary beams upon the mirror as well as upon the specimen can be provided with straightforward means, whereby angular adjustments with a precision of up to 0.1 mrd should be capable of being achieved, and the apparatus should be straightforward in construction and hence economical to provide.